This invention is concerned with improvements in or relating to moisture-curable sealant compositions.
Various sealant compositions are available which are intended to be cured by exposure to atmospheric moisture. For example moisture-curable sealants are known which are based on isocyanate-terminated polyurethanes or based on silicone polymers. Whilst such products yield seals of good quality, they are accompanied by technical or economic disadvantages. For example, sealants based on isocyanate-terminated polyurethanes are unsuitable for packaging and storage in plastic cartridges as evidence of curing of the sealant in such packages is apparent after several months storage. In those cases where a bubble-free seal is essential, precautions must be taken to alleviate bubble formation as a result of production of carbon dioxide during the curing process. Also, heat-resistance of the seals formed is only moderate in many cases. Sealants based on silicone polymers generally have highly desirable properties and yield seals of high quality which perform well under many conditions of use; in particular it is possible to produce a clear, transparent seal and to achieve excellent ultra violet light stability using sealant compositions based on silicone polymers. Such compositions are, however, expensive.
Among objects of the present invention are to provide a sealant composition curable by atmospheric moisture to form a resilient seal at ambient temperatures and based on comparatively cheap raw materials, and to provide a sealant composition having a desirable blend of properties for convenient application and which is capable of cure by atmospheric moisture to provide seals of desirable quality.
It has been proposed to provide polymers having hydrolysable silyl groups by addition reaction between unsatuated polymers and for example chlorosilanes. It has also been proposed to provide polymers bearing hydrolysable silyl groups by addition reaction between unsaturated acrylate monomers and unsaturated silane monomers. Addition reactions generally require particular techniques, reaction conditions and controls in order to procure polymers of required structure and properties, and we would prefer to use a process involving condensation reaction using techniques familiar in the art of condensation polymerisation.
It has been proposed to provide a silane-modified alkylene alkacrylate copolymer comprising at least 50 mol percent alpha olefin units and polymerised units containing a hydrolysable silane radical attached to the polymer backbone via an ester, thioester or amido group. Such copolymer materials generally are solids of comparatively high glass-transition temperature and are not suitable as atmospherically-curable sealant compositions for application at room temperature, not only because they tend to cure to provide products of insufficient rubberiness for many sealant uses but also because their application characteristics and poor adhesive properties are inappropriate for sealant uses.